Peanut seeds are significantly different than other agronomic seeds and have presented some exceedingly difficult problems as relates to the application of pesticides or fungicides to the seed prior to planting.
The skin or testa of the seed is a very important and essential part of the peanut seed, but is fragile and subject to damage, depending upon the method and materials used in treating the seed.
The testa will be recognized as the thin and delicate membrane which embraces the peanut and oftentimes flakes off or is intentionally removed when peanuts are eaten. The testa provides the peanut embryo protection and also supplies essential nutrient enzymes to the germinating seed. The testa contains tannin, pectin and lipoids, and crystals of nitrogenous substance. Partial loss of the seed coat or testa reduces the likelihood that the peanut seed will germinate; and complete loss of the seed coat or testa makes it unlikely that there will be normal germination of the seed. Plants from seeds without the testa have significantly less vigor and produce significantly less yield than plants which grow from normal seeds with the skin or testa in place.
The susceptibility of seed coat damage and loss is dependent upon the type of the peanuts. Spanish and Bunch Type peanuts are more susceptible to damage than Runner Types.
The seed coat or testa also varies considerably in different types of peanuts. In the Spanish peanuts, which are some of the smaller peanuts grown in the United States, the seed coats or testa are relatively smooth and considerably smoother than the testa or seed coat of the Runner Types of peanuts which are generally somewhat larger or of an intermediate size as compared to the smaller Spanish peanuts. The largest peanuts are the Bunch Type peanuts, and these Bunch Type peanuts have seed coats which are considerably more wrinkled and less smooth than the testa of the Runner Type peanuts.
In order to minimize the likelihood of damage to the seed coat or testa during treating of peanut seeds, the seeds have been exclusively treated by applying a dry dust to the seed. Applying chemical treatments by a dust presents formidable problems in the application as well as in the handling of treated seeds prior to planting. The dust products have been finely ground or micronized so that it is very difficult to control the dust during application and handling. The recommended rates of usage of these dust products are 20 percent to 30 percent higher than the amount of chemical than the peanut seed can actually retain on its outside surface. The chemicals present in the dust have contact activity only, and as a result, this massive use of the dry chemicals on the peanut seeds does assure complete coverage and good chemical performance.
These chemical dusts used in treating peanuts are considered to be dust toxicants and are therefore the subject of intense interest by safety and governmental authorities. Many of the people who work with the peanut seeds have allergies responsive to the dust or skin conditions which are sensitive to the dust. Of course, the constant exposure to these dust conditions can present a very serious health hazard to the workers who must work with these peanut seeds. All of the people who handle or work with the seeds at various stages of treatment, handling and planting, including processors, truck drivers, dealers and farmers, are subject to these serious health hazards.
When it is considered that approximately 500,000 pounds of dust chemical seed protectants are required in order to adequately treat the amount of seed to plant the U.S. acreage, the excessive use of treatment by approximately 30 percent of this amount of dust chemical seed protectant is a sizable amount of chemical exposure for people involved in the peanut planting industry.
In a processing plant for treating peanut seeds, the actual treating area should have a dust-collecting system so as to remove the excessive dust from the treating area and ducting the dust outside. Clean air standards, established by both Federal and state and local governments require the air in both the treating area and the bagging area of a processing plant be treated and cleaned for minimum employee exposure. In order to fully comply, a totally enclosed air control system would be necessary at a projected cost of $50,000 to $100,000, depending upon the plant size. In view of the fact that the peanut seed processors operate on a very low gross profit margin, expenditures of this magnitude cannot be justified.
In addition, the chemical dust which is used for treating presents considerable problems to the seed processor in terms of applying the correct amount of the treating dust to the seed. Much of this seed treating is carried on in the southern states where high humidity is a frequent occurrence. High humidity causes the chemical dust to become sticky due to the fact that these dust products hydrate quite rapidly when exposed to high humidities. When the dust becomes sticky, measuring of the dust and causing of the dust to flow freely is extremely difficult and of course the amount applied to seeds becomes rather erratic.
When atmospheric conditions are extremely dry, then the problems of static electricity become extremely important in the handling of chemical dusts. Of course, static electricity also inhibits the flow of dust and the application of exact correct amounts to the seeds is extremely difficult.
Accordingly, unless the humidity conditions during processing is substantially exactly correct, flow problems are continually experienced in handling of dust.
The peanut grower who buys the treated seed is presented with varying problems by the problems of the processor. In many cases, the peanut seeds carry either an inadequate or excessive amount of dust. Inadequate amounts of treating dust on the seed result in a lower rate of germination of the seed in the field, and of course a reduced production. When the peanut seeds carry excessive amounts of chemical dust, the excessive amounts of dust present substantial problems to the grower in planting the seeds.
As indicated above, the chemical dusts become sticky under high humidity ambient conditions, which occur frequently during planting time for peanuts. The dust therefore causes the planting equipment to clog to the point of being inoperable or at least erratic in operation. The planter plates used to place individual seeds in the ground will clog to the point where the openings in the plates will not accept a seed so that the spacings between the seeds planted in the ground become non-uniform. Of course, such non-uniform plant spacing in the field will reduce the overall production of the field.
In the past, some attempts have been made to use slurry treatments with wettable powders and water to treat peanut seeds. These attempts provide quite unsuccessful, primarily because of the effect of the water on the very fragile seed coat or testa which, upon being wetted, becomes hydrated quite rapidly. Later, when the testa is permitted to dry, it shrinks substantially and flakes off the peanuts so as to substantially damage the peanut seed for planting purposes.
In the very distinctive seed coat or testa of the peanut seed, the rate of absorption of water or organic solvent products through the testa is quite rapid. The testa has several layers of cells, the outermost layer of cells being essentially empty. In the testa the second layer of cells contains the dense deposit of tannin, pectin, and lipoids; and the inner layer contains the crystals of nitrogenous substance, but not protein. When exposed to water, the testa acts as a sponge and the inflow of water is 20% to 56% greater than the outflow. Water tends to accumulate between the inner testa cell walls faster than the cotyledons can absorb it. This results in interference with normal germination in exclusion of oxygen and accumulation of carbon dioxide. Also, an exomosis of essential nutrients occurs.
The remaining seed with a partial seed coat or testa loss is referred to as a "Bull-Head"; and a peanut seed which has suffered complete seed coat loss is termed a "Bald-Head".
Because of the marked failure to adequately treat peanut seeds with the water based slurry, the treatment of seed by dusting has been the exclusive way of applying fungicides in recent years.